Strange RF issues

[KD8TZC]

I have recently installed a G5RV Jr antenna in the attic so I can work CW on the 40 and 15 meter bands. Previously, I had just used a 10m dipole with a balun.

The coax line running from the basement into the attic co-habitates with the satellite TV line going to the master bedroom. In the master bedroom my wife informs me that when I am on the radio and she is watching tv in our room, it will do all kinds of strange things (change input sources on the TV, and other things). I don't know if the radio is causing the TV to come on or not. The attic where the antenna is, is right above our master suite.

Any ideas what I can do to eliminate this issue? The G5RV was used in hopes that it would give me the bands that I can use, but I don't recall having this issue with the 10m dipole (which was resonant right around 28.4MHz). The G5RV has to use a tuner to get it into an acceptable SWR, so I'm sure it is radiating garbage off the feed line.

Would a ferrite choke on the TV help, and if so, where would I put it (on the coax for the TV, power cord, etc)? I don't seem to be having any issues with the Satellite box acting strange, just the TV. Would a balun at the point of the coax and the ladder line for the G5RV help?

Thanks

John

 

[nd5y]

Radio Frequency Interference (RFI)

 

[prcguy]

A G5RV really needs a common mode choke at the transition from balanced line to coax, especially on bands other than what it's designed for. A full size G5RV was designed as a 20m antenna that would provide a reasonable match to coax and a Jr version would be for 10m.

The balanced line must be kept away from any other wiring or metal, so if your running it parallel with sat TV cables your probably inducing a lot of common mode RF into your TV system.
prcguy

 

[KD8TZC]

The balanced line must be kept away from any other wiring or metal, so if your running it parallel with sat TV cables your probably inducing a lot of common mode RF into your TV system.
prcguy

Thanks... so you mention parallel with the sat tv cables... would perpendicular or some other crazy layout be better? The thing is, I'm not picking up anything on the Satelite reception... this seems to only be affecting the TV and not the SAT TV Box, so I don't know if the Sat TV feed line is bringing in the issues, or if the G5RV is radiating out strong enough to just affect the TV itself. You might have a good point though on adding a common mode choke though and to see what that can do to improve the situation. I really wish I could mount this outside, but I bet I would have some other issue then.

 

[LtDoc]

Sat TV cable, TV cable, or whatever, it amounts to too much RF in close proximity. There are a number of ways to reduce that RF level, which to use just depends on what's most convenient/possible for you. Distance is the 'best' 'cure', but that's almost never an easy solution.
If you can isolate the RF's entry route it may be possible for you to keep that RF out of it. The part that a lot of people don't realize is that the antenna it's self is the largest contributor to that 'too much RF' thingy, NOT necessarily the feed line from that antenna.
Good luck, hope it works out for you.
- 'Doc

 

[prcguy]

Doc is right about direct radiation from the antenna being the main source of interference in your case since the antenna is right over your head and TV. You still have to keep the balanced antenna cable maybe 6in or a foot away from anything metal and cross other cables at right angles since its sensitive to its surroundings.
prcguy

Thanks... so you mention parallel with the sat tv cables... would perpendicular or some other crazy layout be better? The thing is, I'm not picking up anything on the Satelite reception... this seems to only be affecting the TV and not the SAT TV Box, so I don't know if the Sat TV feed line is bringing in the issues, or if the G5RV is radiating out strong enough to just affect the TV itself. You might have a good point though on adding a common mode choke though and to see what that can do to improve the situation. I really wish I could mount this outside, but I bet I would have some other issue then.

 

[KD8TZC]

Okay guys, thanks. So that creates a bit of a paradox in the fact that I want the antenna to send out RF energy, but not interfere with the TV. I guess I keep coming back to a lowpass filter which seems to be designed to prevent interference with TV's, phones and stereos. Anyone have any experience with them? I was looking at a few of the reviews on another site and the Bencher YA1 looks to be a better one. I think the first thing to look at though is how I have the wires up top. There is nothing I can do about the two coax lines that share a parallel run from the basement to the attic, but once they get into the attic I should check to ensure they don't cross each other and if they do that they do it on a right angle. OR, I can just take the darn G5RV down and make a tuned fan dipole or something. That might actually be less expensive than the lowpass filter.

 

[nd5y]

Low pass filters only work if the RFI is caused by harmonics that fall within the frequency range that the TV receives. If the RFI is from close proximity to a transmitting antenna or a radiating feedline then a low pass filter won't do anything.

 

[LtDoc]

A low-pass filter on the radio and a high-pass on the TV may help, I wouldn't make any large bets on it though. Try it and see?
- 'Doc